TRIANGLE is a Calypso application dedicated to interoperability.

It is based on a very simple principle:

  • The portable object (card, SIM card, USB key, etc.) is interoperable; it means that the customer may use it in all transport networks which are Triangle members.
  • The transport titles and contracts remain specific, and are not shared between the different operators; it means that Triangle requires no clearing system between them.

Consequently, Triangle is very simple to implement.

TRIANGLE answers mainly to two needs:

  • Interoperability between two different tariff areas (2 regions for example) for regular users.
  • Interoperability for occasional users who spend a few days in a city or a region.

TRIANGLE is a Calypso application within the portable object, beside the local application which is used daily for public transport ticketing by the customer. The specificity of Triangle application is that the secure keys are shared between all operators which are Triangle members (personalization, reloading and validation keys). Consequently, all the Triangle operators may use the Triangle application to register and validate their own tickets in the portable object of the customer.

Of course, it requires the operators to strictly respect some mandatory rules, in term of security requirements and also limited functional requirements, particularly not to delete a valid transport title from another operator.

Each operator Triangle member decides which transport titles are offered to the customer through the Triangle application. For example, he may decide to limit them to titles for occasional users, such as single tickets, one-day tickets, etc. and to interregional tickets, etc.


A Triangle customer case

In order to better understand how it works, let’s take a concrete example of a customer using the possibilities of Triangle.

“I live in the Brussels area, and I am a daily user of public transport in this city, taking the train from SNCB and the metro from STIB. So I have a MOBIB card, the unified card for all transport networks in Belgium. Of course, my monthly season ticket within my MOBIB card is accepted by both SNCB and STIB (it is tariff interoperable).

All MOBIB cards include a TRIANGLE application; so I know that I can use my personal MOBIB card in all other transport networks which are TRIANGLE members.

I have to go to Lille, in France, for 3 days, and I know that Lille is a Triangle member: I go to Lille, free of mind, with my MOBIB card; in the Lille station, I go directly to a ticket machine, take my Mobib card and reload it with a 3 days ticket of Lille transport. This ticket is registered within the Triangle application; of course it is accepted on all Lille validators.

It avoids me having to buy a specific media for my ticket and makes really my trip easier.”

With the new possibilities offered by the distant reloading systems on Internet or on mobile phones, the Triangle service may be much better, offering a really seamless solution for the customer. Let’s again take the same example:

“Rather than buy my Lille ticket at a vending machine in the Lille station, I prefer to prepare my trip in Brussels: I connect on the Internet to the reloading web site of Lille, and, with my MOBIB card connected to my computer, I buy and load in the Triangle area the 3 days Lille ticket. It avoids me having to waste time when arriving at the Lille station, to look for the vending machine, or to make a queue.”


TRIANGLE technical

Find all technical description of TRIANGLE, and particularly all the security mechanisms, in the TRIANGLE Specifications document.

Below is the typical representation of the file organization of a card with local and Triangle applications.



How to join TRIANGLE?

If you are an operator or a transport authority which intends on using TRIANGLE, there are some requirements to follow:

  • Of course, to have implemented Calypso for your ticketing system (!)
  • To fill in the form of CNA member registration and to send it, indicating that your interest is to join Triangle. If you are already a CNA member, you use the same form and mention it by checking the appropriate box. You may see all information about CNA membership in the CNA Membership tab.
  • To fulfill the requirements which are described in the TRIANGLE contract, about security and rules of usage. By signing this contact between you and CNA, you will engage in respecting all these requirements towards the whole community of Triangle members. Please note that this contract has already been signed by numerous authorities and operators, and that no more modifications to its content are possible.
  • The acceptance as a Triangle member is submitted to and validated by the assembly of the Triangle members.


If you need complementary information, please call the following number:

+33 (0)1 77 11 81 16 or send a mail to

Please send the signed contract to the following address:

Calypso Networks Association
Rue Royale, 76/2
B 1000 Brussels



Your Triangle membership will be definitively validated after receipt of your payment for CNA membership (by bank account transfer).






How to implement TRIANGLE?


The complete operational procedure to implement Triangle in your system, the management of keys, the certification process are described in the TRIANGLE Best Practices document.


To ensure a better level of interoperability, CNA proposes a set of mandatory tests to be realized at the level of the implementation of Triangle in a ticketing system, in order to ensure that the applicative software respects the rules fixed for a normal behavior of the sale terminal and a compliant management of the contract area within the card.

Find here the guidelines for Triangle conformity

For more information, you can send an email to